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[Hpilot]

Hi
New to the forum.
I'm trying to set up my photo lab( hobby use) using a PID controller. The controller I understand but when it comes to the mechanism that allows either hot or cold water to help keep a constant 68f it gets a little tricky. There are temperature control units on the market but they outside my price range.
Open to other suggestions, ideas and experiences,
Thanks
Howard

[Kkane]

Thanks for posting your question here.

Most of the PID only comes with one main output and several additional alarm outputs. For your case, you can consider using its main output to drive hot water (PID controlled), and alarm output to drive your cold water (only ON/OFF control, as protection). In other word, your system is mainly controlled by hot water (heating), and if the temperature is too high somehow, cold water will be enabled as protection.

If you want to use main output (PID control) to control both hot water and cold water, it will be 1) difficult to find  a PID with two main outputs, and expensive 2) hard to tune the settings, because these two outputs will be affected by each other.

If you decide to use on/off valve to control hot water flow, you can use SYL-2342. If you decide to use proportional value to control hot water flow, you can use SYL-2381-mA.

[Hpilot]

Thanks for the reply(info). I realized that it might rather difficult.
It's probably easier to run the volume of cold water needed and control the constant temp with hot water.
My source for cold water, the city water mains is larger than my source for hot water, my hot water tank.
I do think that I need proportional flow control of the hot water.
Any suggestions on proportional low control valves?

[Kkane]

Johnson control and Belimo carry many proportional valves and actuators.

Yes, it will be simper to fix one output (like cold water) and adjust the other one (like hot water).